My own suggestions are more in the Congress of Vienna – Treaty of Versailles tradition: Cede everything east of the Vorskla and Dnipro rivers to Russia. This includes Crimea, Kharkiv, and Donbas. Allow EU troops [which really means French] to be stationed in the rump Ukraine, but not any troops associated with NATO. This would be too much of an insult to Russia.

Odesa may be largely Russophone, but Ukraine needs to hold on to it as an outlet to the Black Sea. The rump Ukraine would also be permitted to annex Transdinestria. The rest of Moldova would be given a choice as to whether to join Romania by plebiscite, or not.